The present invention relates to a stationary induction electric apparatus such as a transformer or a reactor, and particularly to a stationary induction electric apparatus in which an iron core is configured using a winding iron core.
Most of stationary induction electric apparatuses such as transformers or reactors have iron cores configured using magnetic material, and a structure called “winding iron core” has been widely used, particularly, for an iron core of a stationary induction electric apparatus with a relatively-small capacity of a few MVAs or lower to improve workability. The winding iron core is generally configured by circularly bending laminated magnetic metal ribbons cut in a strip shape. In the case of a winding iron core having the simplest structure, the magnetic metal ribbons with the same width are laminated to configure the winding iron core. In this case, the cross-section of the winding iron core that is orthogonal to a closed curve drawing the circle of the iron core is generally formed in a rectangular shape.
The winding of the stationary induction electric apparatus having the iron core is wound around the outer edge of the cross-section of the iron core as close as possible. It is reasonable to maximize the space factor that is a ratio of the area occupied by the cross-section of the iron core to the area occupied by the winding. The dimension of the main body of the stationary induction electric apparatus and the loss can be reduced by maximizing the space factor. Accordingly, a winding is wound in a rectangular shape in many cases in the case of a winding iron core having a rectangular cross-section. Alternatively, a winding is wound in an oval shape or in a racetrack manner in many cases due to workability such as bending of electric wires configuring the winding.
Further, it is required for a winding to withstand electromagnetic force generated when current accidentally flows. In general, when the capacity of the stationary induction electric apparatus is increased, the electromagnetic force becomes large. When the electromagnetic force to withstand becomes large, a circular winding is generally economical to satisfy the electromagnetic force resistance as compared to that formed in a rectangular, oval, or racetrack shape.
Thus, a circular winding is selected for a stationary induction electric apparatus with a relatively-large capacity of a few MVAs or larger, and the space factor is considerably reduced in the case of an iron core having a rectangular cross-section. Accordingly, the cross-section of the iron core is required to be formed nearly in a circular shape, and an iron core with substantially a circular cross-section of a laminated iron core is adopted for a stationary induction electric apparatus with a large capacity. The laminated iron core configures an iron core circle by combining elements obtained in such a manner that magnetic metal ribbons having various shapes are combined and laminated in a circle of a frame shape. The iron core circle is generally in a frame shape, and the widths of the magnetic metal ribbons configured by laminating the iron core circle are changed to realize an iron core with substantially a circular cross-section.
As described in Japanese Unexamined Patent Application Publication No. 2009-296005, there is a well-known method for a winding iron core in which an iron core with substantially a circular cross-section is realized by changing the widths of magnetic metal ribbons while laminating the same as similar to the laminated iron core, and the iron core is wound in a circular shape to configure a winding iron core with substantially a circular cross-section. Further, the iron core is divided into plural sections in the middle of the circle as described in Japanese Unexamined Patent Application Publication No. 2009-296005.